Water Activity and Moisture Content are two very different parameters which are often confused and misused.
In a meeting today with a manufacturer of coffee capsules and pods, these differences were critical.
– Their whole bean supplier provided each batch with moisture content readings.
– However customers buying the coffee capsules and pods were asking for detailed water activity measurements for each batch. In addition for BRC Food Safety and shelf life validation of the final product, water activity was required.
Why are there these differences and can one measurement be used to determine both values?
Moisture contentis probably the simplest value to understand. It is simply the quantity of water contained in a material. Traditionally measured through loss of weight on drying. This method raises some issues, depending on the drying temperature you may not remove all water or may also remove other non water compounds.
More modern methods resolve these issues and use infra red absorption. This way the water content is directly measured, the method is non-destructive and far quicker.
Moisture content is typically given as a percentage in terms of weight.
Infrared Moisture Measurement – A measure of moisture content through IR adsorption
Water Activity(aW) is a measure of the free water in a sample, and ranges between 0…1. Pure water would have an aW of 1.0. As water activity measures the ‘free’ or ‘active’ water in a sample it is more relevant to growth of organisms, chemical processes, enzyme activity and physical parameters like size and clumping as these are only effected by the water that can be chemically interacted with. Interestingly Water Activity is related to Moisture Content but it is product and temperature specific.
aW… is more relevant to growth of organisms, chemical processes, enzyme activity and physical parameters
Rotronic HygroLab Water Activity Measurement – A measure of the ‘free’ water
What is free water? Water can be bound in materials in two broad ways.
1. Chemically Bound Water. Is bound so tightly that it cannot be utilised by bacteria, enzymes etc. It can be removed through high temperature heating.
2. Free Water. Is bound through weak bonds, structural diffusion, capillary condensation and surface binding. It can be utilised by bacteria and can exchange with the environment, it is also removed through heating.
For instance a whole grape would have the same moisture content as two halves of the same grape. However the aW would be far lower in a whole grape as much of the water is bound inside the grape skin and only made free when the grape is cut in half!
Take a look at our Water Activity white paper or our Knowledge base for more information.
In 2011 Rotronic expanded its range of measurement parameters to include Carbon Dioxide gas measurements and now provides a range of transmitters, loggers, large panel displays and handhelds.
CO2 is becoming an increasing important gas to monitor and control for several reasons. This post will explore some of the science, applications and future trends for this ubiquitous gas…
CO2 and Human Health
CO2 can seriously effect human health. Figure 1 shows this relationship and the possible implications.
Fresh air typically has around 350-450 ppm CO2 however in exhaled air levels increase to around 38,000 – 50,000ppm! Metabolism and exercise can increase the rate of CO2 production.
In the UK we typically have poorly ventilated buildings in addition with increasing drives for energy efficiency, buildings are becoming more air tight and if not managed carefully air change rates can be further reduced. To demonstrate how quickly CO2 can rise through poor ventilation Figure 2 shows a log of CO2, Temperature and Humidity overnight in my bedroom! You can see levels quickly increase to >2400ppm. The rapid drop is due to an opened window
Figure 2 – CO2 levels overnight (CO2 in ppm)
This direct relationship between CO2 and human occupation is a useful tool. It allows building management systems to control ventilation rates precisely to the levels required based on occupation rates. This can significantly reduce energy usage especially with the incorporation of variable speed fans.
Recent projects at Google’s Irish Headquarters and the Apple offices in Cork have used these principles to save energy and improve working conditions for their staff and achieve additional LEED points.
Regulations are increasing for CO2 monitoring. Areas of interest especially we are seeing include Schools, Catering Areas and Car Parks.
If you have any queries relating to CO2 let us know!
It has to start somewhere and for the Rotronic UK blog this is it.
What we hope for this blog, is to start sharing with you the reader some of the more interesting and maybe in cases not so interesting things we come across day in day out as a supplier of measurement instruments, consultancy, training and calibration.
We have a mixed team with diverse interests and expertise, but we are all passionate about quality measurements providing the best solutions to our customers, partners and colleagues.
Please do comment and provide feedback (but be nice!).
Cheers
Jeremy.
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